1. Field of the Invention
The present invention relates to methods and devices for testing the aspheric profile of an aspheric lens.
2. Description of the Prior Art
Recently, attempts have been made to use aspheric lenses in various optical devices to solve a problem to aberration peculiar to a spherical face. It thus becomes necessary to test a manufactured aspheric lens to see whether the lens has the aspheric profile as designed.
Various testing devices using a stylus have been proposed. In such devices the stylus contacts a surface of an aspheric lens. Although the stylus cannot rotate, it can slide toward and away from the lens. The aspherical lens is rotated about an axis passing through the center of a reference curvature radius of the lens. The aspheric profile is tested by the amount of displacement of the stylus which is displaced in the radial direction of the aspheric lens in response to the rotation of the aspheric lens.
In such a conventional device, however, a rotary shaft on which an aspheric lens is mounted and an attachment member on which a stylus is attached are separate members having no correlation therebetween. Therefore, errors associated with the aspheric lens, such as a positioning error relative to the rotary shaft, and errors associated with the stylus, such as a positioning error relative to the attachment member, are caused independently on each other. As a result, these factors may compound to produce a large error as a whole, so that it is difficult to reproduce test results. Further, the diameter of the rotary shaft is not so large and therefore an angular error in rotating the aspheric lens as well as an angular error in measuring the amount of rotation of the aspheric lens unavoidably become considerable values, making it nearly impossible to obtain accurate test results.